Directional speed and distance sensor

ABSTRACT

A method of using a directional sensor for the purposes of detecting the presence of a vehicle or an object within a zone of interest on a roadway or in a parking space. The method comprises the following steps: transmitting a microwave transmit pulse of less than 5 feet; radiating the transmitted pulse by a directional antenna system; receiving received pulses by an adjustable receive window; integrating or combining signals from multiple received pulses; amplifying and filtering the integrated receive signal; digitizing the combined signal; comparing the digitized signal to at least one preset or dynamically computed threshold values to determine the presence or absence of an object in the field of view of the sensor; and providing at least one pulse generator with rise and fall times of less than 3 ns each and capable of generating pulses less than 10 ns in duration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/209,900, filed Jul. 14, 2016, which is a divisional of U.S. patentapplication Ser. No. 14/494,784, filed Sep. 24, 2014, which is acontinuation of U.S. patent application Ser. No. 13/464,706 filed May 4,2012, which claims priority to and the benefit of U.S. ProvisionalApplication Ser. No. 61/549,029 filed Oct. 19, 2011 and 61/638,173 filedApr. 25, 2012. The disclosures of these priority applications are herebyincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

What is described is a directional speed and distance measurement sensorbased on a time of flight ranging technique that can be used to detectobjects in a zone of interest such as automobiles near an intersectionstop bar, access control device, or a parking space. The sensor can alsoact as a transponder and can be combined with in-vehicle devices andother transponders and can be deployed as a network.

BACKGROUND OF THE INVENTION

The use of time-of-flight technology in the field of slow movingvehicles or persons in a narrow and defined zone of interest in closeproximity to the sensor is not common. Light travels at slightly lessthan 1 foot per nanosecond in air. When ranging short distances, such asthose required when detecting vehicles in a parking space or adjacent toa traffic signal stop bar, the pulse width needs to be very short,otherwise there will not be a separation between the transmit pulse andreceive pulse. For example, aircraft radar's pulse widths tend to be inthe microseconds range and they do not work for nearby objects, such aswhen the planes are low overhead.

If used in a time-of-flight mode, parking sensors need to have atransmit pulse of typically 1-3 nanoseconds duration to have adequateseparation between transmit and receive windows. At these pulse widths,the emitted spectrum becomes very broad up to or above 1 GHz.

There is not a greater than 1 GHz block of spectrum anywhere thatregulatory agencies like the FCC allocate for such purposes as spectrumis a very valuable resource. At some extremely high frequencies (>60GHz), there are blocks of spectrum potentially large enough, but theyare difficult to use economically with present technologies.

There is a however a “general class” spectrum, under FCC Part 15(15.209) between intended for such low emissions that there is nopossible interference to anyone else. This requires emitters to emitabout one trillionth of power of a cell phone. This has been usedprimarily for emitters that emit inside a closed metal tank (whereoutside the tank the emissions meet the spec).

The need exists for a sensor using time of flight radar that passesstringent regulatory FCC frequency limits for the first time to detectmovement in short distances or close proximities.

SUMMARY OF THE INVENTION

The described invention is better suited for certain measurements,especially using a battery operated device to detect and measure objectssuch as automobiles or persons that can either be moving or stationary.Other sensing technologies exist, such as Doppler techniques with Radar,Laser, or Ultrasound, Frequency Modulated Continuous Wave techniqueswith Radar, Laser, Infrared, or Ultrasound, Time of flight ranging withUltrasound, etc., but these techniques do not lend themselves well tosituations that have slow or stationery objects and in outdoorenvironments. True time-of-flight ranging with radar or laser has beennot possible until now to adapt for these measurements due to theproximity of the object being sensed, which imposes extremely tighttolerances for the transmit pulse and receive windows and thedifficulties in separating the transmit burst from the received signal.The present invention discloses techniques that make it possible for atime-of-flight ranging sensor to be used for detection and measurementof properties of objects such as automobiles in a defined zone ofinterest, especially in outdoor environments such as a parking space orroadway.

For many applications, narrowly defining a zone of interest and beingable to discriminate whether an object is present within that zone andmeasure its properties is important. For example, in a Red Light Cameraapplication, being able to photograph a vehicle at a consistentposition, immediately upstream of and very close to the stop bar iscritical to ensure consistent image capture and to maximize theviolation capture rates; for a parking application, it is important thatmarked boundary of the parking be treated as a hard zone edge and thatobjects within the parking space are detected reliably and objectsoutside are excluded reliably; at a lane access control point, it isimportant that the vehicle's back or front be detected in a precise spoteach time, so that the camera can capture the license plate reliably.

There is also a significant need in many applications to uniquelyidentify a vehicle at a parking space or an access control point. Forexample, this information can be used to provide discounts, preferentialtreatment of vehicles, or to apply different enforcement or businessrules. One elegant, economical, and effective way of accomplishing thisis to combine the sensor's low power transmission with data and achieveone way or two communications with a compatible in-vehicle device. Thedisclosed invention makes this possible by combining a range ofdisclosed features including low power transmissions that are repeatedfrequently, highly localized transmissions in the zone of interest,techniques that use the transmission and reception capabilities in theradar to also communicate low data rate information such as an uniquevehicle identification, and techniques that enables the sensor todistinguish between target object radar signatures from transmissionsfrom the in-vehicle devices. The disclosed techniques also make itpossible for very low powered in-vehicle devices that can operate onsmall battery or solar power.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part ofthe specification. The drawings, together with the general descriptiongiven above and the detailed description of the exemplary embodimentsand methods given below, serve to explain the principles of theinvention. The objects and advantages of the invention will becomeapparent from a study of the following specification when viewed inlight of the accompanying drawings, wherein:

FIG. 1 shows a representation transmit pulses and the receive windows.

FIG. 2 shows as example deployment in a roadside parking or movingvehicle application.

FIG. 3 shows the ability of the sensor to be mounted differently thusadapting to different geometries and installation requirements.

FIG. 4 shows the sensor integrated with wireless communications in anyof the example locations, communicating via a gateway or repeater, orvia cellular network, represented by tower.

FIG. 5 shows an illustration of a video output if the receive windowstiming is continually swept in relation to the transmit for a fixedobject and its envelope.

FIG. 6 shows examples of transmit bursts.

FIG. 7 shows an example location of a sensor on top of a pole with abubble that overlaps an area immediately upstream of an intersectionstop bar.

FIG. 8 shows a sensor mounted adjacent to a parking space with a bubblethat is contained within the parking space being monitored.

FIG. 9 shows a parking space monitoring application wherein the sensoris positioned to detect the change in ranging distance as the vehicle isapproaching or receding.

FIGS. 10 and 11 illustrate profiles of data points obtained bysuccessive ranging samples by elements 27 and 28 for a vehicle entry andexit event respectively.

FIG. 12 shows an example implementation wherein the time window of thereceive window with respect to the transmit is fixed and in which thereceive may be larger than the transmit pulse duration; phase variationin the reflected signal relative to the transmit pulse caused by thetarget's movement can be used to measure vehicle speed and also acorroborative evidence of a vehicle movement event; for example, thiscan be used to definitively exclude reflected signals from stationerytargets.

FIG. 13 shows a block diagram illustration of a wired connection betweena parking meter and the sensor. The sensor may be attached to the meteror may be a modular detachable part. Element 29 represents a wiredconnection such as through discrete wires or a cable.

FIG. 14 shows a configuration in which the sensor is embedded within aparking meter, access control device, or any other device that can beactive or passive, including a parking space marking sign or acommunications device.

FIG. 15 shows a plurality of sensors that are wirelessly coupled to aplurality of network elements such as gateways, cellular towers, parkingmeters, access control devices, imaging devices, and to remote serversand databases.

FIG. 16 shows an example in which the transmit pulses are frequencymodulated for the purposes of using an overlapping or fixed receivewindow with respect to the transmit or communicating low data rateinformation to or from an in-vehicle device.

FIG. 17 shows a sensor with a plurality of radiating elements, eachradiating preferentially in a different direction so as to covermultiple zones of interest or multiple regions within a zone ofinterest.

FIG. 18 shows a sensor configuration with a plurality of radiatingelements, at least one of which has a radio frequency absorber materialused for the purposed of calibrating the sensor.

FIG. 19 shows a vehicle with its in-vehicle device within range of asensor to enable one-way or two-way communication.

FIG. 20 shows some of the possible locations for locating an in-vehicledevice which include inside the vehicle chassis or outside near thefront or rear of the vehicle.

FIG. 21 shows a plurality of sensors deployed close to each other withsome of the bubbles overlapping used in an unmarked parking application.

FIG. 22 shows a subterranean deployment of sensors, each with aplurality of radiating elements positioned to detect occupancy andvehicle movement with apriori expectation of the vehicle's position.

FIG. 23 shows the schematic diagram of the sensor.

FIG. 24 shows example pulses used for the transmit pulse and the localoscillator pulse used in a receiver local oscillator corresponding tothe receive window; the timings indicated are for example purposes only.

FIG. 25 shows an example spectrum of emission generated by a shortpulse.

FIG. 26 shows a schematic of a timing generator to generate the transmitpulses and synchronize the receive windows with respect to the transmitwindow.

FIG. 27 shows an example discrete digital timing generator with adiscrete receive window timings that are digitally controlled by amicroprocessor

FIG. 28 shows an example of a digitally controlled timing generatorcontrolled by a digital signal controller.

FIG. 29 shows an example of an analog timing generator that can be usedwith both the base frequency as well as the reference voltagescontrolling the pulse widths are set by a microprocessor.

FIG. 30 shows a flow diagram related to the detection of characteristicchange by the sensor.

FIG. 31 shows a block diagram of the operation of a payment system(parking meter).

FIG. 32 shows that the sensor unit may have a hardwired interconnect tothe payment system (parking meter).

FIG. 33 shows a sensor unit that is detached from the payment system.

FIG. 34 illustrates a block diagram of a sensor unit that is attached tothe parking meter, and generally corresponds to FIG. 32.

FIG. 35 illustrates a block diagram of a sensor unit that is detachedfrom the parking meter, and generally corresponds to FIG. 33.

FIGS. 36 and 37 show respective sensor block diagrams of the detachedsensor and the attached sensor embodiments.

FIGS. 38 and 40 show the sensor unit detached from the payment systemand communicating with a server system.

FIG. 39 shows the sensor unit attached to and communicate with thepayment system (parking meter).

FIGS. 41 and 42 show how the sensor circuit and the meter circuit areseparate circuits, and not two logical portions of a single circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to exemplary embodiments andmethods of the invention as illustrated in the accompanying drawings, inwhich like reference characters designate like or corresponding partsthroughout the drawings. It should be noted, however, that the inventionin its broader aspects is not limited to the specific details,representative devices and methods, and illustrative examples shown anddescribed in connection with the exemplary embodiments and methods.

This description of exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. The word “a” as used in theclaims means “at least one” and the word “two” as used in the claimsmeans “at least two”.

A true time-of-flight radar essentially transmits a pulse of a radiofrequency carrier wave using a transmit antenna and then waits for areceive echo and measures the time between the transmit (Tx) and receive(Rx) pulses.

Time of flight Radar and Laser ranging technology is extensively usedfor a variety of applications, including the detection and rangemeasurement of airborne or sea surface objects, distance measurementfrom space, etc. When used for relatively distant objects, measurementerrors caused by the transmit pulse duration, receive burst timingerrors, etc., are not significant and the transmit burst can be of along enough duration to contain the spectral width of the transmissionwithin a relatively small range. However, ranging with objects at ashort distance, say less than 20 feet, places significant limitations onthe measurement techniques that are not easily overcome.

There is a significant need for reliable, short distance measurements ofobjects such as automobiles or persons within a small and defined zoneof interest for a variety of applications. For example, in a Red LightCamera application, being able to photograph a vehicle at a consistentposition, immediately upstream of and very close to the stop bar iscritical to ensure consistent image capture and to maximize theviolation capture rates; for a parking application, it is important thatmarked boundary of the parking be treated as a hard zone edge and thatobjects within the parking space are detected reliably and objectsoutside are excluded reliably; at a lane or driveway access controlpoint, it is important that the vehicle's back or front be detected in aprecise spot each time, so that the camera can capture the license platereliably.

Doppler techniques using radar or infrared laser can be very accuratefor measurement of velocity and are widely used in speed radarapplications, but are unable to detect a slow moving or stationeryvehicle or object. Magnetic flux measurements are often used todetermine the presence or absence of a vehicle in a parking spot, butthese suffer from lack of spatial resolution as the measurement areacannot be tightly constrained within a defined space and these cannotwork with objects with small or no ferrous content. Magnetic inductiontechniques require considerable power to operate and are not suitablefor battery operated areas, such as a remote installation, a roadsideinstallation, or in any areas where electric grid supply is notavailable or not economically feasible. Frequency modulated continuouswave ranging techniques using infrared laser and radar suffer from theinability to differentiate spurious reflections and clutter fromreflections from the target object. Ultrasound techniques suffer frominaccuracies due to changes in ambient air density and interference fromambient noise sources. Thermal imaging techniques suffer if the objectis not guaranteed to have a thermal signature, such a car that is parkedfor a length of time and has cooled down to the surrounding temperatureor a heavily clothed person not exposing any warm skin. Visual imagingsuffers from processing complexity and interference from changingambient lighting conditions and extraneous light sources.

The disclosed invention uses techniques that make it possible for truetime of flight ranging to be used for detection and measurement ofobjects such as automobiles from short distances. Many challenges intime of flight ranging need to be overcome to fit this purpose, which isaccomplished by this invention.

Radio waves and infrared light travel in air at close to the speed oflight in vacuum, i.e., slightly less than 1 foot per nanosecond. By thetime these waves to hit and reflect off the object to be measured at itsclosest range, the transmit burst should be completely silenced and thedevice needs to be ready to listen for the reflected signal in thereceive mode. Since the waves travel the path from a sensor to thetarget and back, they travel twice the ranging distance which can beapproximated to one foot of measured distance per two nanoseconds. Thisfactor establishes the minimum pulse width of the transmit pulse and thetradeoffs involved between near object measurement and pulse length. Inpractice however, the transmit pulse needs to be quite smaller than theminimum range to be measured to provide for a sufficient gap between thetransmit burst and receive window as well as to ensure adequate rangeresolution.

There are however some rare exceptions to this such as when a largetarget is in close proximity and a reflecting object on the other sideof the sensor and the waves from the transmit burst are made to bounceback and forth repeatedly and effectively behave like a longer rangemeasurement that would tolerate a longer transmit burst.

There is however, one embodiment of the present invention that uses adifferent technique for targets that are extremely close to the sensor.In this embodiment, the transmit and receive windows overlap or a singlewindow is used, for example, with a regenerative detector. Since thephase of the received signal is uncontrolled with respect to thetransmit, there is a chance that the received signal would work tocancel the transmit and prevent detection of the object. In thedisclosed embodiment, this problem is overcome by either using aplurality of radiating elements so that a plurality of distances to thetarget object can be measured or to modulate the transmit pulse usingfrequency or phase modulation.

FIG. 1 shows a representation transmit pulses 2 and the receive windows.In practice, a large number of transmit pulses are sent and the receivewindows adjusted or swept in relation to the transmit pulse. The receivewindow timing shown by a, b, c and d (3, 4, 5, and 6 respectively). Inthe illustration, the change in the receive window timing with respectto the transmit pulse is shown with 3, 4, 5, and 6 of differentmagnitudes.

FIG. 2 shows as example deployment of a directional sensor 30 accordingto the present invention (referred to hereinafter as “sensor”) in aroadside parking or moving vehicle application. Element 10 denotes aparking lane and 8 and 9 are sensor locations. Element 7 shows arepresentation of a bubble in the zone of interest. It will beappreciated that the directional sensor 30 of the present invention isprovided for the purposes of detecting the presence of a vehicle or anobject within a zone of interest on a roadway or in a parking space.

FIG. 3 shows the ability of the sensor 30 to be mounted differently thusadapting to different geometries and installation requirements. Element11 shows a pole mount, where the sensor 30 is mounted on a pole. Thepole may be shared with parking meter or other street infrastructure.Element 12 denotes the sensor 30 mounted on a curb face or a curb top.Element 13 shows the sensor 30 embedded under the surface. This type ofmounting can also be used when the bubble is directed at an angle.

FIG. 4 shows the sensor 30 integrated with wireless communications inany of the exemplary locations, 14, 15, and 16, communicating via agateway or repeater 17, or via cellular network, represented by a tower18.

In order to reduce the ranging uncertainties from a long transmit burstand to be able to measure the range at short distances, a transmit pulsetrain is employed that includes a brief burst of a carrier wave, notmore than 6 nanoseconds, but more typically 1-3 nanoseconds effectivewindow width. While ideally this transmit burst may have the carrierwave at full amplitude instantaneously and have a rectangular envelope,in practice, the carrier wave envelope may take a triangular,trapezoidal, or another shape (for example, 23). See FIGS. 5 and 6 forexamples of these different wave envelopes. Specifically, FIG. 5 showsan illustration of a video output 20 if receive windows timing iscontinually swept in relation to the transmit for a fixed object and itsenvelope 19. FIG. 6 shows examples of transmit bursts. Element 21 showsan burst with a rectangular envelope, and elements 22, 23, and 24 showtriangular, sinusoidal, and other envelope shapes.

FIG. 7 shows an example location of the sensor 30 on top of a pole witha bubble 26 that overlaps an area immediately upstream of anintersection stop bar. FIG. 8 shows the sensor 30 mounted adjacent to aparking space with the bubble 26 that is contained within a parkingspace being monitored. FIG. 9 shows a parking space monitoringapplication wherein the sensor 30 (with the bubble 26) is positioned todetect the change in ranging distance as the vehicle is approaching orreceding.

FIGS. 10 and 11 illustrate profiles of data points obtained bysuccessive ranging samples by elements 27 and 28 for a vehicle entry andexit event respectively.

A very short transmit burst of the order of a few nanoseconds willoccupy a very large portion of the radio spectrum. In order to complywith applicable rules for such transmissions, the transmit power levelsneed to be extremely low. This typically means that the received energyfrom just one or several bursts is not sufficient to make a reliabledetermination due to low signal to noise ratios. In order to increasethe signal to noise ratio to acceptable levels, a large number ofsamples, which may be in the thousands to over a hundred thousandsamples or more need to be integrated. This needs to be accomplishedwithin a reasonable measurement time. In addition, the duty cycle of thedevice needs to be adjusted to maximize the signal to noise ratio whilestill being a low duty cycle device. These goals can be accomplished byusing a high pulse repetition frequency for the transmit burst, forexample between 5 and 30 MHz.

Generally once receive window per transmit pulse is employed. Thereceive window timing can be continuously swept in relation to thetransmit pulse (see elements 3, 4, 5, 6 in FIG. 1) in order to generatea modulated video waveform with a fixed or adjustable sweep rate.Precise and repetitive control over the receive window's timing inrelation to the transmit pulse is critical and can either be achieved byusing the transmit burst's timing as a reference or using precisionclocking circuitry.

Using an adjustable receive window so as to be able to control thereceive window to a desired range of interest and adjust the integrationperiod for a particular range window is an advantage. For example, in aparking space detection application, when the space is vacant, a longreceive window of the order of 10-20 ns can be employed just to scan ifthere is any received signal within this window and when a signal isfound, the receive window can be further narrowed down to more preciselyrange the target vehicle. The advantage of this technique is that itwill shorten the duration of the sensor active time when the space isvacant or there is no change in state, which will be the vast majorityof the time, and hence will enable the sensor operation withsignificantly lower power consumption and is one of the disclosedadaptations that will help a longer battery life.

In many cases it is desirable to have the ability to arbitrarily adjustthe receive window's timing in relation to the transmit pulse. Forexample, this will enable a software controlled intelligent sensor torange only a narrow window of interest or selected discrete time ranges.This will enable the sensor to detect a narrower set of ranges in turnreducing the amount of time the sensor is active and reducing powerconsumption. For example, a two or three dimensional bubble can bedefined and the sensor can only be ranging at the edges of the bubble todetect if there is any vehicle entering the bubble; or if a vehicle isparked, as an example, 3 feet distance from the sensor, the sensor cannormally range only around that previously measured vehicle distance andonly upon a change in status, the sensor can range other ranges. Inaddition, the adjustable range capability can be used by softwarecontrol to integrate selected range windows over longer or shorterperiods of time to provide higher or lower signal to noise ratios. Forexample, in a noisy environment, if potential reflections are seen at agiven range, but the object reflections do not clearly differentiateform the noise, the software can hover over that and adjacent rangewindows for longer periods of time and get a less noisier signal inorder to make a determination of the object's presence and range.

FIG. 12 shows an example implementation wherein the time window of thereceive window with respect to the transmit is fixed and in which thereceive may be larger than the transmit pulse duration; phase variationin the reflected signal relative to the transmit pulse caused by thetarget's movement can be used to measure vehicle speed and also acorroborative evidence of a vehicle movement event. For example, thiscan be used to definitively exclude reflected signals from stationerytargets. FIG. 13 shows a block diagram illustration of a wiredconnection between a parking meter and the sensor 30. The sensor 30 maybe attached to the meter or may be a modular detachable part. Element 29represents a wired connection such as through discrete wires or a cable.FIG. 14 shows a configuration in which the sensor 30 is embedded withina parking meter, access control device, or any other device that can beactive or passive, including a parking space marking sign or acommunications device.

FIG. 15 shows a plurality of the sensors 30 (in locations 31 and 32)that are wirelessly coupled to a plurality of network elements such asgateways, cellular towers, parking meters, access control devices,imaging devices, and to remote servers and databases. FIG. 16 shows anexample in which the transmit pulses are frequency modulated for thepurposes of using an overlapping or fixed receive window with respect tothe transmit or communicating low data rate information to or from anin-vehicle device.

It is critical in many applications that a precisely defined area ofinterest is monitored and it is important that objects within the areaof interest are detected reliably and objects outside the area ofinterest are reliably excluded, irrespective of the size of the objects.In practice, it is common to encounter situations where there may be asmaller target object within the area of interest and a largernon-target object just outside. For example, a sensor monitoring a zonenext to a stop bar in one lane, needs to avoid triggering even if a busis present in the adjacent lane and a parking space sensor in a streetparking situation needs to avoid triggering even if there are buses ortrucks in the traffic lane immediately adjacent to the space. Usingprecise ranging, it is important that the sensor is able ignore effectsof reflections from the non-target object. It is possible to have awell-defined volume of space or a “bubble” that corresponds to the zoneof interest. This is accomplished using a well-characterized directionalantenna and precise ranging by having a precise control of the receivewindow in relation to the transmit burst. The ability to orient eitherthe antenna or the entire sensor such that the bubble covers an optimalvolume over the desired space of interest will also be necessary in manyapplications.

Since a large number of received samples need to be integrated, it isdesirable for the integrator output to be digitized for manyapplications. The integrator output can be treated as an analog inputvoltage into an analog to digital converter and digitized. In someapplications, where the receive timing is swept in relation to thetransmit, a modulated video waveform is generated with the envelopecontaining the object signature. The digitized signal can then beevaluated via software or hardware to see if it meets the criteria of anobject signature and to extract presence and range information from thedigitized signal. There can be multiple objects in the sensor field ofview and in some cases, their object signatures may overlap. Dependingon the application, the center of the object profile or it is beginningor another point can be used for range determination. In some cases aone-bit digitizer can be used comprising of a comparator and indicatewhether the integrator output exceeds a certain threshold level whensampling a desired range window. The circuitry for digitalization andevaluation can employ components such as, but not limited to,microcontrollers, analog to digital converter integrated circuits, fieldprogrammable gate arrays and other programmable logic devices, analogcomparators and operational amplifiers, or simple active or passivecomponents.

In many cases, it is desirable to extract the envelope from the videosignal as that is a lower frequency signal and easier to work with.Envelope information can be generated using a demodulator, low passfilter circuit or similar or by a variety of software algorithms basedon filtering, peak detection or other techniques.

For some short range sensing applications, a situation often exists whenthe object is too close requiring the receive window close to thetransmit pulse such that the object signature at the integrator outputis mixed with the transmit spike or its ringing or decay. This calls forspecial techniques to digitize the decay and comparing the decay toknown profiles using profile matching or curve fitting techniques insoftware and determining the variance from a predefined decay model inorder to extract object signatures from said integrator output. Adifferential technique may also be employed here by comparing the objectprofile with a simulated free space profile. The free space simulationcan be accomplished using an absorber material that ensures there is noreflected signal. This can be accomplished by mechanically inserting anabsorber material in the radiative path, but is more easily accomplishedusing an additional antenna element that may be coupled with anadditional transmitting element.

There are some applications in which it is desirable for the thresholdfor object determination to be recalculated periodically from within thesensor. Such recalculation can happen either for every measurement orperiodically as a self-calibration mechanism. Drift in integrator outputfor example, can be detected by computing the average of the sample,detecting flat regions of the integrator response and comparing withprevious measurements, or using a known range window that is guaranteednot to have an object present. For remote deployments, it is often notpossible to guarantee that there will not be any object inside thebubble during calibration, and therefore, there are constraints in howthe self-calibration mechanism can be setup. In a parking spacedetection application, for example, it is often not possible to clearout the parking space when installing, testing, or performingmaintenance on a sensor. In those cases, it may be possible to use an RFor Infrared absorbing medium, depending on the type of sensor, tosimulate a no target object condition. In one embodiment, a plurality ofRF stages and antenna elements that can be switched can be used and anRF absorbing medium can block all radiation from one of the antennaelements. When switched to this element, a device can simulate a freespace condition and thereby serve as a calibration reference.

In some cases, a material that is a known dielectric can be used to fillthe spaces inside or just outside the antenna to help shape the antennabeam width to be optimal for the application. Such “beamforming”techniques allow us to use smaller antennas and shape the antenna fieldof view to best match the spatial area of interest and will help inachieving a narrow, defined spatial zone of interest. Also a pluralityof antenna elements in combination with one or a plurality of RF stagesmay be used in an arrangement where some of them are may be switched tobe able to steer the antenna. For example, if two adjacent spaces arebeing monitored by a sensor, that may be accomplished using two antennaelements that are switched based upon the desired space to monitor; orfive antenna elements can be used to detecting 5 sub-zones across twoparking spaces can help identify a variety of conditions, such asoverlapped parking, bad parking situations, etc. This technique isespecially useful when detecting vehicles in unmarked parking spaces.

There are other errors however, that cannot be corrected only using aself-calibration approach. Clutter around the transmitter is a majorsource of error. Many sources can contribute to clutter including cablesand wires around the sensor, the sensor housing, nearby objects that mayget moved into the bubble but do not by themselves make the space beingmonitored unusable for the targets of interest. In such cases, ideallythe sensor will be able to detect a permanent changed condition andignore the clutter and get object signatures in relation to the clutter.This approach will provide some mitigation against clutter. Softwarealgorithms and heuristics may be employed to determine which changes inreturned signal profiles represent clutter and which changes representthe intended target and it is important in some cases to separate thetwo. Such determination can be done by using data related to strength ofthe reflected signal, the duration and persistence of the object, thedistance from the sensor, etc.

In some applications, it is important to distinguish between astationery object from transient objects that are slow moving. Forexample, in a parking occupancy detection application, it may bedesirable to count only automobiles that are fully parked and ignoresensor activations from persons walking across the spaces or shoppingcarts being moved across. Successive profiles from the sensor may becompared to ensure that the object signature is present and consistentfor a period of time and classify the target as stationery or transientand apply suitable business rules.

Many applications will require the sensor and associated electronics,including communication components to use minimal power consumption andhave a long battery life or be charged by solar cells. A prioriknowledge about expected probability of an object state change can beused in some cases to dynamically adjust the interval between datasamples as a way of reducing battery life. For example, in a parkingapplication, if the peak hours or high turnover hours for parking areknown beforehand the sensing in those hours can be more frequent thanothers. At night time or during unregulated parking hours, when the datais less important, the samples can be stopped or taken at a reducedfrequency. In some cases, this data can be self-generated at the sensorby analyzing historical patterns thus making the sensor self-adaptive.

In many cases, various software filters are employed in conjunction withthe digitization of the video or the envelope signal. The videowaveform's signal to noise ratio can be enhanced by a narrow bandpassfilter and further low pass filtering or peak detection techniques cangenerate a low noise envelope waveform that contains information aboutthe object profile. Such filtering can be performed with in time domainor in frequency domain. It should be noted that the filtering andenvelope detection can be generated using hardware techniques as well.If the envelope signal is digitized or computed by software filters, itcan also be further filtered using low pass or bandpass filters toreduce noise and obtain the object signature.

In many cases, determining the speed and direction of travel of thetarget object within the detection zone is important. This can beaccomplished using multiple successive range measurements to discernwhether the object is moving closer to or away from the sensor. This canbe used very effectively in a parking monitoring situation to determinewhether a vehicle is arriving at a space or leaving the space. Themultiple successive range measurements combine to form of profile of theobject's movement within the area of interest. This information can becommunicated to a remote system using wired or wireless means and beused as further evidence of the object's movement. The additionalinformation can be used as corroborative evidence in an administrativeadjudication process or in a court of law. When detecting persons on awalkway for example, this method can be used to determine theirdirection of travel. This is also useful in situations where there istravel in more than one direction within the area of interest and onlyobjects traveling in some of those directions are being monitored. Forexample, in an automated gate operation application, vehicles coming intowards the gate need to be identified separately from those moving awayfrom the gate.

The practical installation of the sensors imposes many challenges on thedesign. Places where the sensors are mounted such as roadways, walkways,etc. differ in construction materials, physical geometry and availablemounting locations and other site specific considerations such asdrainage, other uses, etc. It is important that the sensor design isflexible so as to be able to work at a particular site. In addition, thesensor may interface using wired or wireless means to other devices,such as parking meters, cameras, or gate control devices. A sensor thatcan be configured for various mounting locations would be highlydesirable. This can be accomplished by means of separate enclosures,optimal direction of the antenna, and software configurations such thatthe detected object and clutter profiles are appropriate for theparticular mounting arrangement.

FIG. 17 shows a sensor with a plurality of radiating elements 34, eachradiating preferentially in a different direction so as to covermultiple zones of interest 33 or multiple regions within a zone ofinterest. FIG. 18 shows a sensor configuration with a plurality ofradiating elements 34, at least one of which has a radio frequencyabsorber material used for the purposed of calibrating the sensor.

FIG. 19 shows a vehicle 42 with an in-vehicle device within range of thesensor 30 to enable one-way or two-way communication. FIG. 20 shows someof possible locations 38 for locating the in-vehicle device whichinclude inside the vehicle chassis or outside near the front or rear ofthe vehicle 42.

FIG. 21 shows a plurality of the sensors 30 deployed close to each otherwith some of the bubbles 26 overlapping used in an unmarked parkingapplication. FIG. 22 shows a subterranean deployment of the sensors 30,each with a plurality of radiating elements positioned to detectoccupancy and vehicle movement with apriori expectation of the vehicle'sposition. A plurality of the sensors 30 so deployed could cover theunmarked set of parking spaces.

The directional sensor 30 for the purposes of detecting the presence ofa vehicle or an object within a zone of interest on a roadway or in aparking space, according to the present invention, is schematicallyshown in FIG. 23 and comprises:

means for transmitting a microwave transmit pulse such that a totaldistance occupied by the pulse in air is less than 5 feet;

a directional antenna system to enable the transmit pulse to be radiatedpreferentially towards a detection area;

an adjustable receive window to receive received pulses, said receivewindow being precisely timed in relation to the transmit pulse with thereceive window being similar or different (smaller) in duration than thetransmit pulse;

means for integrating or combining signals from multiple received pulsesto increase a signal to noise ratio;

an amplifier and filter for amplifying and filtering the integratedreceive signal to further increase the signal to noise ratio;

means for digitizing the combined signal using an analog to digitalconversion process;

means for comparing the digitized signal to preset or dynamicallycomputed threshold values to determine the presence or absence of anobject in the field of view of the sensor; and

at least one pulse generator with rise and fall times of less than 3 nseach and capable of generating pulses less than 10 ns in duration forcontrolling the transmit pulses and receive windows.

An exemplary schematic diagram of the sensor 30, shown in FIG. 23,comprises a directional antenna 43 and a core timing generator 44capable of generating sharp pulses with rise and fall times less thanabout 3 ns each and small pulse widths, typically less than 10 ns. Thetiming generator 44 may in turn be controlled or synchronized via adigital signal controller (or a microprocessor) 46. In some embodiments,the core timing generator 44 may use an internal reference oscillator.The timing generator 44 controls the transmit and receive windows andtheir relative timing and depending on the embodiment, provides sweep,fixed, or discrete or arbitrarily adjustable capabilities. The sensor 30further comprises a Mixer and Regenerative receiver 48 that representsan RF block including an RF oscillator tuned to a desired centerfrequency, a low noise amplifier, to amplify incoming reflected signals,a mixer/detector that can use regenerative techniques to generate a lowfrequency voltage that is a function of the reflected RF and amplifiedby the low noise amplifier. The low frequency voltage or current isfurther filtered through analog signal conditioning means 50. Adigitizer 52 can be a single bit digitizer using a comparator or ananalog-to-digital converter (ADC) circuit. The ADC 52 can be integral toa microcontroller or a digital signal controller or be a part of acircuit block on its own. The digitized signals can be further filtered,conditioned and processed through digital filtering/processing means 54and software means 56. Various business rules and heuristics such as forreconfirmation checks, vehicle based rules, and others are executedthrough the software means 56. A power management and control block 58is used to regulate one or more voltages required by the various partsof the circuit as well as to turn off power to the parts of the circuitsin idle mode when they are not required, including in-between samples.

The sensor output can be a data stream, or a digital or analogindication of vehicle presence or absence. This signal can beelectrically coupled to another device including but not limited toparking meters, cameras, or gates, or can be coupled to a communicationdevice such as a wireless modem or repeater. The information from thesensor including presence detection, range, direction, and profiles, canbe sent to remote server for storage and further processing.

In one embodiment of the sensor 30, a figure of merit related to theconfidence level of the object detection and measurement can becalculated using one or more of the data available in the sensor,including the returned signal strength, consistency in readings inmultiple readings, distance of object detected, signal to noise ratiocalculated in the device, The calculated confidence level can betransmitted to a remote server along with the detection and measurementresults and used by an end system such as an enforcement camera, parkingmeter, or an adjudication process.

In one embodiment of the sensor, the receive window is kept constantwith respect to the transmit during a part of or the whole measurementduration. In this mode, a phase variation of the reflected RF is causedby the movement of the vehicle. This phase variation is sampled usinganalog or digital means and is used to compute the velocity of thevehicle. In addition, this information can be used as corroborative datato definitely establish a vehicle ingress or an egress event in anadministrative adjudication process or in a court of law.

In another embodiment of the sensor, the receive window may be adjustedto overlap with the transmit or a single window may be used for bothreceive and transmit with a suitable pulse width. This mode isparticularly useful for detecting objects at very close range, forexample, within 2 feet from the sensor. In a further variation of thisembodiment, a plurality of RF stages and antenna elements can be used ina switched manner such that the RF path to the object traverses aplurality of lengths and if an object is present, at least of thelengths will result in a suitable phase difference between the reflectedand the transmitted pulses to enable detection using a regenerativecircuit or other means.

The sensors are typically deployed as a network of sensors covering aplurality of parking spaces or road lanes. The wireless or wiredcommunication means electrically coupled to the sensor can be consideredas a part of the sensor network communicating to one or more remoteservers and databases.

The sensors may contain baseline profiles that are a function of theranging distance, temperature, the integration time, or other parametersavailable from the sensor. Such profiles may use a combination ofconstant pre-determined data and data derived from the sensor either onetime prior to installation or dynamically through a processor means.

The sensor may be programmed with distances to range, time intervalsthat correspond to ranging distances, or geometrical properties of thezone of interest. The software means in the sensor can be used to derivepulse timing information or sweep rate information from the programmeddata and this may further be used to control the sensor operation in thedesired mode of operation. The programmable parts of the sensor and itsconfiguration, including profiles, zone information, bubble and ranginginformation, sensitivity and threshold values, and the softwareexecutable code and its configurable elements can all be wirelesslydownloaded using an appropriate protocol from a remote server. Suchwireless downloads can be initiated by the server when the wirelessmodule electrically coupled to the sensor is active. Such downloads mayalso be initiated by the processor means electrically coupled to thesensor querying the server for suitable downloads. For example, thesensor may be programmed to query the server once a day to check for anyupdates of executable or configuration elements and upon server responsecommence the download protocol.

The sensor processor means may further contain a hardware or softwarewatchdog to detect software or hardware malfunctions and automaticallyreset itself. In addition, a backup copy of an older or provenexecutable and configuration elements may be stored in persistentstorage coupled to the processor means and in case of any malfunctions,the processor means may be programmed to try the backup copy. Thesefeatures of wireless downloads and self recovery from faults are veryimportant in applications where the sensors are remote and unattended orembedded in the road surface or curb and access to sensors is notavailable or is very expensive.

The low power features and battery operation in the present inventionlend the sensor to be permanently installed in the road pavement or inthe curb. The directional nature of the sensor enables us to configurethe sensor for a wide range of geometries, and to locate the sensor onthe curb or on a meter pole, outside the zone of interest. The abilityto deploy the sensor based on the site characteristics is of great valuein operating the sensor.

The sensor may be programmed to send its diagnostic data periodically toa remote server using the wired or wireless communication means that iscoupled to the processor means. Such information may be used toreconcile the sensing data and monitor the health of the sensor. Exampledata elements that can be sent for this purpose include occupancy timeor ratio, counts of vehicle entry and exit events, battery voltage,count of samples taken, sensor active times, signal strength or qualitymetrics of the wireless link and other data available at the sensor.

The sensor signals or data communicated through the wired or wirelessmeans can be used by a parking meter to provide free time or to removetime from the meter or to provide information for enforcement personnel.For example, when a vehicle enters a parking space near a retailestablishment, it may be desirable to provide s set amount of free time,say 15 minutes and the patron can be allowed to pay a meter to add tothat. In this configuration, upon the sensor detecting a vehicle entryevent, the data or signals it communicates using wired or wireless meanscan update the meter time. This can be accomplished whether the sensorfirst communicates to a remote server via a wireless network, includingany gateway components, or the sensor send the signals or data to aparking meter using wireless or wired means.

In one embodiment of the sensor, the sensor can also act as atransponder to communicate with in-vehicle devices or handheld devicesof maintenance and enforcement personnel. Modulation techniques tomodulate a stream of pulses are well known, including pulse positionmodulation, pulse width modulation, phase modulation, frequencymodulation, etc. The sensor pulses can be modulated to transmitinformation indicating the sensor operation or other data such as thelane number, space number and enforcement hours and tariff to in-vehicleor handheld devices.

In another embodiment, the sensor can further be wirelessly coupled withan in-vehicle device capable of transmitting back to the sensorpertinent information, such as vehicle type, a unique identification ofthe vehicle, or classification of the vehicle.

The in-vehicle device may be mounted in the interior or exterior of thevehicle chassis and may have a plurality of antennas. Alternatively, aplurality of in-vehicle devices may be used to cover the front and backof a vehicle. Since in some parking spaces, vehicles can park either ina front-in or a back-in configuration, a single in-vehicle device withantenna may not be sufficient.

The in-vehicle device can use an RF amplifier to amplify the transmittedpulses and at least one fixed or programmable delay element andretransmit the amplified RF. This technique enables mirroring theincoming RF from the sensor and simulates a target at various ranges.The received profile from such a delayed mirror transmission can beeasily distinguished from a physical target by its profile as well asthe specific time slots that the in-vehicle device transmits. As anexample, the in-vehicle device may transmit a code at specific rangingintervals, that will form a unique signature of an in-vehicle device. Inaddition, the code can contain a specific identification of the devicethat indicates unique vehicle identification, vehicle class, etc. Inanother embodiment, the in-vehicle device can have a dynamicallyprogrammable delay code to transmit bits of data back to the sensoracross multiple time sequences. This method will enable a longer code tobe transmitted to the sensor.

In one embodiment, the sensor can adjust the receive window to preventan unfavorable fixed phase between the return signal and the transmitsuch that they cancel each other and prevent detection. Alternatively,the in-vehicle device may contain circuitry or logic to alter the delayto avoid this issue.

The identification of the vehicle, including unique vehicleidentification, can be used by devices that are coupled with the sensoror a sensor network to grant preferential or differential treatment tothe vehicle or to apply business or enforcement rules. This can be inthe form of a gate access, lane access, discount schemes in a toll laneor a parking application, or to apply different business rules based onthe vehicle identification or vehicle class received. The data can alsobe encrypted between the in-vehicle device and the sensor to preventtampering.

The exchange of information between the sensor and an in-vehicle devicemay be packaged as or may conform to a communications protocol.

In one embodiment, the sensor can have a plurality of antenna elementswith either a single RF stage or a plurality of RF stages. Thiscapability also serves multiple purposes. For example, in a parkingsituation, two spaces may be covered by a single sensor. In anotherexample, two zones covering the two edges of a parking space and anothercovering the middle may be used. If a vehicle is parked improperly inthe space, two of the three zones will be occupied. If two adjacentvehicles are parked too close to the space under detection, the twoedges will be occupied and the middle will be vacant. In a roadwayconfiguration, a similar technique may be used to accurately determinethe lane of travel. There are many applications where the parking spacesare unmarked. In these situations, it is not possible to predict where avehicle will park in relation to the sensor. The available parkingsurface can be sampled as multiple smaller zones with one or moresensors and the resulting data can accurately determine the occupancystatus and where a vehicle is located.

In one embodiment, the sensor is used as a low power monitoring devicein a roadway or an entry way. When the sensor detects a vehicle or anobject it is used to power on or wake up one or more additional devices,such as radar, Lidar, imagers, physical access control devices such asgates or barriers, electronic access controls, and communicationdevices. This is very useful in a battery powered application, such asportable traffic counting, portable speed enforcement, or surveillanceapplication on a roadway or an entryway.

The processor means, software means, timing and digital controlcircuitry, analog filters and processing circuitry, RF circuitry andantenna elements and other functional modules can reside in one or moreboards that may be directly connected or interlinked through cables andconnectors.

In accordance with the foregoing description, the present inventionprovides a method of detecting change in occupancy state over a definedzone of interest on a roadway or parking space by computing the distancein 2 or 3 spatial dimensions from a directional ranging sensor to eachboundary point of the zone of interest and adjusting the rangemonitoring parameters to monitor at or near the boundary distances toquickly detect when any vehicle enters the zone boundary, wherein thedistance computation to the boundary may be manually set in hardware,preset in software, or dynamically computed in software logic.

The present invention further provides a method of programming adirectional ranging sensor used to detect the occupancy of a zone ofinterest in a roadway or parking space with programmable parameters suchas location of sensor, width of traffic lane or parking space, thatcorrespond to the geometric properties of the roadway zone of interestor parking space and the sensor programmatically computing themonitoring parameters for optimal detection.

Additionally, the present invention provides a method of using a roadwayor parking space sensor that modulates the transmit pulses of the sensorwith additional information, such as lane number, maximum speed, spacenumber, hours of operation, maximum duration of stay, or other pertinentinformation.

The invention further defines the step of using any of pulse positionmodulation, phase modulation, frequency modulation, pulse widthmodulation or similar techniques.

According to the present invention, an in-vehicle device is capable ofreceiving the transmissions and sending a time-coded signal to thesensor that simulates range information is used with the in-vehicledevice locking phase and frequency with the sensor transmission. Thein-vehicle device transmits a unique vehicle identification data to thesensor.

The sensor transmits information back to the in-vehicle device that isall or in part derived from all or a portion of the vehicleidentification data obtained from the in-vehicle device. Additionally,at least one of the sensor transmission and the transmission from thein-vehicle device may be encrypted for security purposes. With theinvention, the unique vehicle identification is used to automaticallyprovide roadway or parking services such as preferential access,permitted access, discounts, or other services. Additionally, the uniquevehicle identification is used to detect scofflaw, stolen vehicles, orother vehicles of interest.

In accordance with the invention, the sensor transmission rate may beincreased when a vehicle ingress event is detected to receive theinformation from the in-vehicle device.

The in-vehicle device may includes a low-noise radio frequency front-endamplifier and at least one delay circuit. A plurality of sensors and aplurality of in-vehicle devices may have communications compatibility inorder for a given sensor to communicate with any of the vehicles withsuch capability. The in-vehicle device may include two or more antennaelements to cover the front and back of a vehicle. The plurality ofin-vehicle devices may be used within a vehicle and they share all or apart of their unique identification number in order to determine thatthey belong to the same vehicle.

In accordance with the invention, a method of using a roadway or parkingspace sensor is provided that combines or colocates the sensor with aradio frequency transmission device to transmit additional information,such as lane number, maximum speed, space number, hours of operation,maximum duration of stay, sensor operational status, or other pertinentinformation.

Further, the invention provides a method of using a directional, radiofrequency time of flight sensor for the purposes of detection of themotion or the presence or absence of an automobile on a zone of intereston a roadway or in a parking space that includes a plurality of antennaelements, aligned in a plurality of directions, with the ability toswitch between the elements to detect multiple zones of interest ormultiple portions of a given zone of interest.

The invention further includes selectively giving more weight to somezones or portions of a zone as detected by the plurality of antennaelements. The plurality of antenna elements may be provided with an RFabsorber element to be used as a calibration reference.

A software means may be used to compute the difference between thecalibration reference and the measured profile of a target object inorder to determine the presence and range of the target object.

The sensor may contain any combination of a processor means, a softwaremeans, timing means, digital or analog filter means, and powermanagement means where in each of these functions may reside on aplurality of circuit boards that are electrically coupled usingconnectors and cable means.

A plurality of sensors may be deployed in unmarked parking spaces with aseparation less than one car length in order to detect vehicles parkedin unmarked spaces. The plurality of sensors each with a plurality ofantenna elements may be deployed in unmarked parking spaces such thatthe combines zones cover the full area of parking spaces and thesoftware means is used to discriminate vehicle position and occupancystatus.

The sensor is operated by at least one of battery power or solar power.

The sensor may be embedded permanently within the roadsurface or curb orattached permanently to the curb. The sensor may be programmed to usevariable sample rates based on estimated frequency of activity in thezone of interest, speed of movement within the zone of interest, or timeof day.

The sensor can be programmed to send diagnostic data to a remote serveror meter periodically. The occupancy information from the sensors isused to detect lane use or parking violations and transmitted wirelesslyto any field devices including, field enforcement aids, or dynamicstreet signage.

The processing means maybe coupled with a failure recovery mechanismsincluding hardware or software watchdog mechanism to detect devicefailures and backup copies of executable code and configuration elementsin persistent storage.

Successive profiles may be obtained using a set of ranging samples arecompared for a period of time to determine whether the target objectdetected is stationery or a transient object.

FIG. 24 shows exemplary pulses used for the transmit pulse and the localoscillator pulse used in a receiver local oscillator corresponding tothe receive window; the timings indicated are for example purposes only,while FIG. 25 shows an exemplary spectrum of emission generated by ashort pulse. In other words, FIG. 25 shows an example schematic of thetiming circuitry using a clock edge synchronization and a Pulse WidthModulation generator with two channels. The first channel is used withan adjustable delay to generate the transmit pulse of fixed oradjustable width. The second channel has an adjustable delay in relationto the same reference clock edge and has an adjustable pulse width. Thetwo pulses may be added together to generate the transmit and receivewindows control for the RF stages.

FIG. 26 shows a schematic of a timing generator to generate the transmitpulses and synchronize the receive windows with respect to the transmitwindow. Specifically, FIG. 26 shows an exemplary discrete digital timinggenerator with a discrete receive window width that is digitallycontrolled by a microprocessor. This implementation incorporates areference oscillator to serve as the clock source, a fixed first pulseto for the transmit pulse and selectable delays that can be selected bya processor means and combining the two pulses to form a single pulsestream of transmit and receive pulses.

FIG. 27 shows an example discrete digital timing generator with adiscrete receive window timings that are digitally controlled by amicroprocessor. Specifically, FIG. 27 shows an exemplary digitallycontrolled timing generator controlled by a digital signal controller.The transmit and the receive pulses are generated by the digital signalcontroller and use programmable pulse widths and timings.

FIG. 28 shows an example of a digitally controlled timing generatorcontrolled by a digital signal controller, while FIG. 29 shows anexample of an analog timing generator that can be used with both thebase frequency as well as the reference voltages controlling the pulsewidths are set by a microprocessor. Specifically, FIG. 28 shows anexemplary analog timing generator that can be used with both the basefrequency as well as the reference voltages controlling the pulse widthsare set by a microprocessor through an analog-to-digital converter thatmay be integrated within the microprocessor or be an external component.The first comparator generates an edge with fast slope to serve as atiming reference. The reference voltages set at the second and thirdcomparators determine the time delay in their respective outputsrelative to the first comparator output. The difference in time delaysrealized through the logic gate enables controlled and narrow pulsewidths.

As shown in FIG. 30, the sensor unit that detects a characteristicchange (e.g., of frequency and/or amplitude) of the signals that itprocesses. A change of one or more signal characteristics is associatedwith a change in status as to whether a vehicle is present or not. Thesensor unit may take several readings per second. In one embodiment ofthe sensor unit, each new reading of the sensor unit is compared withthe previous reading of the sensor unit. As shown in FIG. 30, when thesensor 30 detects a change, relative to a previous reading, of one ormore signal characteristics (associated with a change of a vehicle beingpresent to a vehicle being not present, or from a vehicle being notpresent to a vehicle being present), the sensor data is formatted, andthe sensor data that is associated with the current status (of a vehiclebeing present or not) is transmitted from the sensor unit to either thepayment system (e.g., a parking meter) or a remote server, as describedfurther below. FIGS. 38-40 also show that the data associated with avehicle being present (or absent) are transmitted from the sensor unitto either the payment system (e.g., a parking meter) or a remote server.FIGS. 41 and 42 show how the sensor circuit and the meter circuit areseparate circuits, and not two logical portions of a single circuit.

FIG. 31 shows a block diagram of the operation of a payment system(parking meter). As shown in the embodiment in FIG. 31, when the sensorunit detects a change in status from a parking space being vacant tobeing occupied, the sensor unit will zero out any time that may beremaining on a parking meter from a vehicle that was previouslyoccupying the parking space associated with that parking meter. When thetime on the meter elapses, the meter provides a visual indication thatthe parking space is unpaid and unoccupied. The payment system providesthe visual indication apart from the sensor unit which, as describedabove, only detects a change in status that is associated with a changeof a vehicle being present to a vehicle being not present, or fromvehicle being not present to a vehicle being present. The presenceindication and meter payment data are also transmitted from the parkingmeter to a server via the Internet. The sensor unit itself does notstore data associated with a vehicle being present (or absent), and thatthe sensor unit is not designed for the purpose of storing the sensordata. The sensor unit is designed and intended to transmit the dataindicative of a change in status to a parking meter (or to a server viathe Internet in other embodiments) as fast as the sensor unit is able todo so.

FIG. 32 shows that the sensor unit may have a hardwired interconnect tothe payment system (parking meter). FIG. 32 also indicates that in anoptional configuration, the sensor unit can be detached from the paymentsystem, which is the case with multi-space meters. In the hardwiredinterconnect embodiment, the payment system (parking meter) queries thesensor unit to obtain sensor data, and that the meter (and not thesensor unit) utilizes the sensor data to determine if there is a changein status that is associated with a change of a vehicle being present toa vehicle being not present, or from vehicle being not present to avehicle being present. FIG. 39 shows that the sensor unit can beattached to and communicate with the payment system (parking meter), andFIGS. 38 and 40 show that the sensor unit can be detached from thepayment system and communicate with a server system.

FIG. 33 shows a sensor unit that is detached from the payment system,and is positioned within or just below the surface of the street todetect the change in status that is associated with whether a vehicle ispresent or not. When the sensor unit detects a change in status, thesensor unit transmits the change of status wirelessly to the paymentsystem or to a server by using a wireless interface to communicate withthe server. In the detached sensor unit configuration, the sensor unitinitiates the transmission of data associated with a change of statusthat is associated with whether a vehicle being present to a vehiclebeing not present, or from vehicle being not present to a vehicle beingpresent, upon detecting such a change, and that the data are transmittedto and stored in the parking meter or server.

FIG. 34 illustrates a block diagram of a sensor unit that is attached tothe parking meter, and generally corresponds to FIG. 32. FIG. 35illustrates a block diagram of a sensor unit that is detached from theparking meter, and generally corresponds to FIG. 33.

FIGS. 36 and 37 are respective sensor block diagrams of the detachedsensor and the attached sensor embodiments. The detached sensorschematic (FIG. 36) differs from the attached sensor schematic (FIG. 37)in that the detached sensor schematic has a power management and batteryblock, whereas the attached sensor schematic only has a power managementblock. The attached sensor embodiment does not require a separatebattery because it is powered by the same power source that is utilizedby the parking meter. In addition, the detached sensor unit has awireless communication module that allows the detached sensor unit totransmit data to the parking meter or the server, as indicated, forexample, on FIG. 33. Apart from these differences, the followingdescription of detached sensor configuration also applies to theattached sensor configuration.

As shown on FIG. 36, the detached sensor block diagram includes blocksor modules for power management and battery, RF (radio frequency),beamforming and antenna, digital processing, analog processing, andwireless communication functions. The power management and battery blockis used to manage and control the power used by the detached sensor unitin order to extend the life of the battery used by the detached sensorunit. For example, the power management and battery block would ensurethat the wireless communication module is not constantly transmitting toa parking meter or to the server, as such a transmission would shortenthe life of the battery.

The method according to the present invention uses a directional sensorfor the purposes of detecting the presence of a vehicle or an objectwithin a zone of interest on a roadway or in a parking space. Thismethod according to the present invention comprises the following steps:

-   -   a) transmitting a microwave transmit pulse such that a total        distance occupied by the pulse in air is less than 5 feet;    -   b) radiating the transmitted pulse by a directional antenna        system to enable the transmit pulse to be radiated        preferentially towards a detection area;    -   c) receiving received pulses by an adjustable receive window,        said receive window being precisely timed in relation to the        transmit pulse with the receive window being similar or        different in duration than the transmit pulse;    -   d) integrating or combining signals from multiple received        pulses to increase a signal to noise ratio;    -   e) amplifying and filtering the integrated receive signal to        further increase the signal to noise ratio;    -   f) digitizing the combined signal using an analog to digital        conversion process;    -   g) comparing the digitized signal to at least one preset or        dynamically computed threshold values to determine the presence        or absence of an object in the field of view of the sensor; and    -   h) providing at least one pulse generator with rise and fall        times of less than 3 ns each and capable of generating pulses        less than 10 ns in duration for controlling the transmit pulses        and receive windows.

According to the method of the present invention, at least one of thepulse repetition frequency, transmit pulse width, receive windowduration, and the interval between the transmit and receive windows isadjustable using a digitally controlled circuit or under softwarecontrol from a microprocessor. The receive window, according to themethod of the present invention, is adjusted by software control inorder to dwell on a particular receive time slice region of interest soas to increase the signal to noise ratio of the received measurement.The receive window is also kept longer than the transmit pulse durationwhen the roadway or parking space being monitored is vacant and when anoccupancy change is detected the receive window is made smaller to moreprecisely range the vehicle

Further according to the method of the present invention, the intervalbetween the transmit and receive windows is continuously adjusted usingan analog or digital hardware sweep circuit or under software control.Moreover, the software is programmed to adjust the interval between thetransmit and receive windows to a programmatically determined zone ofinterest. The zone of interest is based on the expected region where achange in occupancy state will happen, including the previously measureddistance of an occupying stationery vehicle, a programmed maximumdistance if the detection zone was previously vacant, or a predictedzone of occupancy if a vehicle is moving.

The receive window, according to the method of the present invention, isadjusted by software control in order to dwell on a particular receivetime slice region of interest so as to increase the signal to noiseratio of the received measurement.

Further according to the method of the present invention, the sensor isplaced at one of (a) a location below the surface of the zone ofinterest, (b) a location above the surface and in contact with the zoneof interest, (c) a location near the surface and adjacent to the zone ofinterest oriented to radiate preferentially towards the zone ofinterest, (d) a location on a raised fixture near the zone of interestoriented to radiate preferentially towards the zone of interest, (e) alocation embedded within a parking meter or an access control device,and (f) a location embedded within a parking space number sign.

Also according to the method of the present invention, the receivewindow is continuously swept at a fixed or adjustable rate with respectto the transmit window in order to generate a video waveform output andoptimize the detection latency and signal to noise ratio, wherein thevideo waveform output is digitized using an analog to digital conversionprocess using a circuit that is electrically coupled to the receiver andintegrator and the digitized output is suitably filtered and compared toa preset or dynamically computed threshold profiles in order to discernwhether there is sufficient returned signal from an object in the fieldof view of the sensor.

Moreover according to the method of the present invention, the transmitand receive windows are pulsed at a rate between 5 MHz and 50 MHz inorder to optimize the signal to noise while ensuring compliance withregulatory limits. Also, when a change of state is determined from thereturned signal, successive sets of samples are taken in quicksuccession to confirm or deny the first determination of change and aconfidence level is computed based on the consistency in readings.

In the method according to the present invention, the filter is one of ahardware filter electrically coupled to the receiver and integrator, anda software algorithm using digitized signals. Moreover, a software orhardware envelope detector is used to extract a lower frequency profileof the received signal from a generated video.

The method according to the present invention can further comprise amode in which the interval between the transmit and receive windows iskept fixed and the vehicle movement will result in a Doppler effect onthe returned signal due to the phase shift of the returned signal inrelation to the transmit and a phase coherent detection is performedreturned signal phase varying in relation to the transmit pulse withvehicle movement and the resulting phase difference to combinedestructively or constructively with the transmit pulse at the detector.Ranging and Doppler detection is used as corroborative data to increasethe confidence of measurement, and the Doppler signal is furtherprocessed to determine whether a change in state event is an ingress oran egress event.

Further according to the method of the present invention, change inoccupancy state and any of the other data elements or available in thesensor on the roadway or parking space is communicated to an externalhost using wired or wireless means, wherein a plurality of sensors arecommunicating to at least one external host using wired or wirelessmeans forming a network of sensors that communicate with the host forthe purposes of data transmission from the sensors, and configuration,monitoring and control of the sensors.

Also according to the method of the present invention, the transmit andreceive windows are fully or partially overlapping in order to detectvehicles at very close distances and the transmit pulse frequency isvaried by using one of (a) frequency modulating the transmit pulse (b)discrete frequency control of the transmit oscillator to generate atleast two distinct frequencies and (c) incorporating a known amount offrequency noise or drift in the transmit oscillator. Also, successiveranging samples are used to determine whether there is a gradual changein object range in order to discern whether a change in state event isan ingress or an egress event and a profile of the ingress or egress iscaptured by multiple ranging samples, wherein the profile obtained istransmitted to an external host using wired or wireless means forstorage.

Further according to the method of the present invention, the time offlight ranging is used as a low power monitoring device and the changeof state determined from the received signal is used to wake one or moreadditional devices, such as a speed measurement device or an imagingdevice in order to manage the power consumption of those devices. Also,a high dielectric material is used inside or near the antenna element toenable a narrow beamwidth in a small antenna package.

Moreover, the method of the present invention further comprises abaseline profile that includes the transmit burst, initial clutteraround the sensor and integrator decay so as to discern the signaturesof close-in objects whose signals are mixed in with the transmit burst,initial clutter, or the integrator decay. In addition, the method of thepresent invention further comprises a temperature compensation of thebaseline profile, including for the initial clutter, integrator decayand noise thresholds.

The foregoing description of the exemplary embodiment of the presentinvention has been presented for the purpose of illustration inaccordance with the provisions of the Patent Statutes. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Obvious modifications or variations are possible in light ofthe above teachings. The embodiments disclosed hereinabove were chosenin order to best illustrate the principles of the present invention andits practical application to thereby enable those of ordinary skill inthe art to best utilize the invention in various embodiments and withvarious modifications as are suited to the particular use contemplated,as long as the principles described herein are followed. Thus, changescan be made in the above-described invention without departing from theintent and scope thereof. It is also intended that the scope of thepresent invention be defined by the claims appended thereto.

What is claimed is:
 1. A battery operated sensor system for detecting apresence of a vehicle or of an object within a zone of interest on aroadway or in a parking space, comprising: a sensing element comprisinga transmitter and a receiver and housed within a sensor enclosure, thesensing element being configured to produce an output that is derivedfrom the duration of a time of flight of at least one traversal of atransmit burst from the transmitter to an object in the parking spaceand back to the receiver and includes a timing generator with a durationof less than 10 ns; at least one of a second transmitter and a secondreceiver collocated with the sensor enclosure that is communicativelycoupled with an in-vehicle device; the in-vehicle device comprising athird transmitter and a third receiver and further comprising a uniqueidentification of a vehicle and being configured to be mounted eitherinside or on the body of the vehicle; and a processor for combiningsensor status information from the sensing element with the uniquevehicle identification, received from the in-vehicle device, to enableidentification of the vehicle to facilitate processing of the vehiclefor one or more of payment, enforcement, data collection, andadvertising purposes.